Method of making a current controlling device including VO{HD 2{B

ABSTRACT

A current controlling device for an electrical circuit including a semiconductor element and electrodes in low electrical resistance contact therewith, wherein said semiconductor element has a threshold voltage value and a high electrical resistance to provide a blocking condition for substantially blocking current therethrough, wherein the high electrical resistance is substantially instantaneously decreased to a low resistance in response to a voltage above said threshold voltage value to provide a conducting condition for substantially conducting current therethrough, wherein the semiconductor element comprises high electrical resistance refractory powder particles substantially individually coated with a thin solid coating of substantially VO2, wherein the high electrical resistance refractory powder particles may comprise SnO2, SiO2, Al2O3, ZrO2 or TiO2 or the like, wherein the thin substantially VO2 coating on the particles is obtained from V2O5 and/or V2O3 in the formation thereof by several methods described herein, wherein the devices may be of the non-memory type or the memory type, and wherein the devices may have an intermediate or partial conducting condition.

United States Patent Fleming et al.

METHOD OF MAKING A CURRENT CONTROLLING DEVICE INCLUDING V0 Inventors:Gordon R. Fleming, Pontiac;

Stanford R. Ovshinsky, Bloomfield Hills, both of Mich.

Energy Conversion Devices, Inc., Troy, Mich.

Filed: Sept. 8, 1970 Appl. No.: 70,155

Related U.S. Application Data Division of Ser. No. 830,581, May 27,1969, Pat. No. 3,588,638, which is a continuation-in-part of Ser. No.809,580, March 24, 1969, abandoned.

Assignee:

References Cited UNITED STATES PATENTS 9/1968 Futaki et al 252/518 X12/1969 Futaki 252/518 X 3/1970 Shimoda.... 252/518 X 'l/1971 Teeg eta1. 252/518 2/1971 Mitsuishi et a]. 252/518 FOREIGN PATENTS ORAPPLICATIONS 9/1936 Switzerland 252/518 Primary ExaminerMichae1 F.Esposito [57] ABSTRACT A current controlling device for an electricalcircuit including a semiconductor element and electrodes in lowelectrical resistance contact therewith, wherein said semiconductorelement has a threshold voltage value and a high electrical resistanceto provide a blocking condition for substantially blocking currenttherethrough, wherein the high electrical resistance is substantiallyinstantaneously decreased to a low resistance in response to a voltageabove said threshold voltage value to provide a conducting condition forsubstantially conducting current therethrough, wherein the semiconductorelement comprises high electrical resistance refractory'powder particlessubstantially individually coated with a thin solid coating ofsubstantially V0 wherein the high electrical resistance refractorypowder particles may comprise SnO SiO A1 0 ZrO or TiO or the like,wherein the thin substantially VO coating on the particles is obtainedfrom V 0 and/or V 0 in the formation thereof by several methodsdescribed herein, wherein the devices may be of the non-memory type orthe memory type, and wherein the devices may have an intermediate orpartial conducting condition.

11 Claims, 12 Drawing Figures J7 15 c J9 I doned METHOD OF MAKING ACURRENT CONTROLLING DEVICE INCLUDING V This application is a division ofGordon R. Fleming and Stanford R. Ovshinsky application Ser. No.830,581, filed May 27, 1969, now US. Pat. No. 3,588,638 which in turn isa continuation-in-part of Gordon R. Fleming and StanfordR. Ovshinskyapplication Ser. No. 809,580, filed Mar. 24,. 1969 (now aban- Theinvention of this application is related to and is an improvement uponthe invention disclosed in Stanford R. Ovshinsky US. Pat. No. 3,271,591issued Sept. 6, 1966. That patent discloses two basic types of currentcontrolling devices, a non-memory type device (referred to therein as aMechanism device) and a memory type device (referred to therein as Hi-Loand Circuit Breaker devices). Both the non-memory and memory typedevices are changed from their blocking condition to their conductingcondition by ap-. plying a voltage above a voltage threshold value. Thenon-memory type device requires a holding current to maintain it in itsconducting condition and it immediately returns to its blockingcondition when the current decreases below a minimum current holdingvalue. The memory type device requires no holding current, it remainihgin its conducting condition even though the current is removed orreversed, and it is returned to its blocking condition by a currentpulse of at least a threshold current value. The invention herein isapplicable to both types-of current controlling devices.

A principal object of this invention is to provide an improved currentcontrolling device for accomplishing the current controlling orswitching functions substantially as performed by the currentcontrolling devices of the aforementioned U.S. Pat. No. 3,271,591.Another object of this invention is to provide a current controllingdevice having an intermediate or partial conducting condition.

Another principal objectkof this invention is to provide improvedmethods for making the semiconductor elements of the current controllingdevices.

The current controlling devices of this invention, while utilizingsubstantially V0 in the semiconductor element thereof, are considerablydifferent in construction, manner of operation and results obtained fromthe Neel effect switching devices of l-landelman US. Pat. No. 3,149,298wherein the devices of said patent utilize pure single crystals ofvarious described vanadiumoxygen compounds, which are thermally biasedclose to selected temperatures for the various selected crystals, whichare thermally cycled above and below said selected temperatures forswitching purposes, and

which have relatively small conductivity differences between theirswitched conditions.

Briefly, the semiconductor elements of the current controlling devicesof this invention which are contacted by the electrodescomprise highelectrical resistance refractory powder particles which are.substantially individually coated with a thin solid coatingofsubstantially V0 Such refractory powder particles them in substantiallycontacting engagement in a carrier such as paint or glass or the like.

Because of the thin coating of the substantially V0 on the highelectrical resistance refractory powder particles, the semiconductorelement has a high electrical resistance in its blocking condition whichis much higher than where crystalline V0 itself would be interposedbetween the electrodes. In this respect, the coated particalizedstructure forms elongated tortuous paths through the coatings about theparticles between the electrodes which are of high resistance. In theinhomogenious polycrystalline coated particles there are no specialrequirements for purity and stoichiometry as would be required in singlecrystals. The current controlling devices of this invention operate atroom temperature and no thermal biasing is necessary. There is noproblem with structural degeneration as is experienced in cycling singlecrystals. Resistivity changes be tween the blocking condition and theconducting condition are much larger than those in single crystals.Field induced electronic excitation without concomitant temperatureincrease sufficient to reach a transition point is also possible toobtain switching of the devices of this invention.

The substantially V0 thinly coated refractory powder particles may beformed in various ways. For example, V 0 powder particles may be mixedwith the refractory powder particles within a moler percent range ofabout 5 to 25% of V0 and heated in a reducing atmosphere to atemperature between the melting point of V 0 and the melting point of V0to melt the V 0 powder particles and form substantially V0 andindividually coat the refractory powder particles with the thin solidcoating of substantially V0 As another example, V O powder particles andV 0 powder particles in substantially equal molar percent are mixed withthe refractory powder particles within a moler percent range of about 5%to 25% of said V 0 and V 0 and heated in a substantially inertatmosphere to a temperature between the melting points of V 0 and V 0and the melting point of V0 to melt the V 0 and V 0 powder particles andform substantially V0 and individually coat the refractory powderparticles with the thin solid coating of substantially V0 By utilizingthe aforementioned mole percent range of 5 to 25% the individual coatingof the refractory powder particles with the thin coating ofsubstantially V0,, is assured so that theresultant product is stillsubstantially in powder or particalized form rather than in a mass formwhich fractory powder particles with said thin coating of substantiallyV0 The V 0 sol. may be formed by suspending V O in water and mixing withH 0 to form a liquid having peroxyvanadates in solution in the water,boiling the solution to decompose the peroxyvanadates back to V 0 tofonn the V 0 sol having the charged V 0 particles colloidally suspendedtherein.

It has been found that by using as the refractory powder particles SnOSiO A1 or ZrO extremely satisfactorynon-memory type current controllingdevices are obtained. It has also been found that by using TiO as'therefractory powder particles extremely satisfactory-memory type currentcontrolling devices are obtained. It has been further found that whereZrO- and sometimes. A1 0 .are used as the refractory powder particlesdouble switching actions may be obtained in a non-memory type currentcontrolling device. In this latter respect, the device switches from ablocking condition to a partially conducting condition upon theapplication of a voltage above a first threshold voltage value, and itswitches from the partially conducting condition to a substantiallyfully conducting condition upon the application of a voltage above asecond threshold voltage value. Such a device is extremely useful incomputer logic circuits or the like to produce additional points ofreference. This device can also be returned from the partiallyconducting condition and the substantially fully conducting conditiondirectly to the blocking condition when the current through the devicedecreases below minimum current holding values.

Other objects and advantages of this invention will become apparent tothose skilled in the art upon reference to the accompanyingspecification, claims and drawing in which:

FIG. 1 is a diagrammatic illustration of the current controlling deviceof this invention connected in series in a load circuit;

FIG. 2 is a voltage current curve illustrating the operation of thenon-memory type current controlling device of this invention in a DC.load circuit;

FIGS. 3 and 4 are voltage current curves illustrating the symmetricaloperation of the non-memory type current controlling device and theoperation thereof when included in an AC. load circuit;

FIG. 5 is a voltage current curve illustrating the operation of thememory type current controlling device of this invention in a'D.C. loadcircuit;

FIGS. 6 and 7 are voltage current curves illustrating the symmetricaloperation of the memory type current controlling device and theoperation thereof when included in an A.C. load circuit;

FIG. 8 is a voltage current curve illustrating the operation of thenon-memory type current controlling device of this invention in a DC.load circuit where the device switches from a blocking condition to apartially conducting condition and from the partially conductingcondition to a substantially fully conducting condition;

FIGS. 9 and 10 are voltage current curves illustrating the symmetricaloperation of the non-memory type current controlling device illustratedin FIG. 8 and the operation thereof when included in an AC. loadcircuit;

FIG. 11 is an enlarged diagrammatic view of the current controllingdevice showing the V0 coated refractory particles arranged between apair of electrodes;

and

FIG. 12 is an enlarged view of the semiconductor material illustrated inFIG. 1] illustrating in more detail the V0 coated refractory particles.

Referring first to FIGS. 11 and 12, the current controlling device ofthis invention is generally designated at 10. It includes asemiconductor material 11 at such as described above arranged between apair of electrodes 12 and 13. The semiconductor material 11 is of oneconductivity type and is. of high electrical resistance and rthe pair ofelectrodes 12 and 13 in as 11 contact with thesemiconductor materialhave a low electrical resistance of transition therewith. The highelectrical resistance refractory powder particles which may comprise SnOSiO A1 0 ZrO or TiO or the like are designated at 40 and the thin solidcoating of substantially V0 forthese, refractory powder particles isdesignated at 41. The VO coating 41 on these refractory particles 40 maybe accomplished in the manner described above. These coatedparticles 40,41 may be formed into the semiconductor element in various ways, as forexample, compacting them into pellets, or incorporating them intosubstantially contacting engagement in a carrier such as paint orglassor the like. The electrodes 12 and 13 may be made to contact thesemiconductor materials 11 in various ways. They may be mechanicallypressed in contact therewith, they may be hot pressed into thesemiconductor material, and they may be deposited thereon by vacuumdeposition, sputtering, or deposition from a solution or the like.Alternatively, the semiconductor material may be deposited on theelectrodes by. brushing, silk screening, painting or the like. The.electrodes'should be good electrical conductors and should not reactunfavorably with the semiconductor material. As for example,-theelectrodes may comprise refractory metals, such as, tungsten, tantalum,molybdenum, columbium or the like, or metals, such as, stainless steel,nickel, chromium or the like. The paint or glass type semiconductorelements have particular utility for use in conjuction withelectroluminescent panels wherein the semiconductor elements'may bereadily applied thereto by painting or silk screening or the like forcontrolling the same.

Referring now to the diagrammatic illustration of FIG. 1, the currentcontrolling device 10 of this invention having the semiconductormaterial 11 and the electrodes 12 and 13 is connected in series in anelectrical load circuit having a load 14 and a pair of terminals 15 andl6for applying power thereto. The power supplied may be a'D.C. voltageor an A.C. voltage as desired. The circuit arrangement illustrated inFIG. 1, and as so. far described, is applicable for the nonmemory typeof current controlling device. If a memory type of current controllingdevice is utilized, the circuit also includes a source of current 17, alow resistance 18 and a switch 19 connected to the electrodes 12 and 13of the current controlling device. The pur pose of this auxiliarycircuit is to switch the memory type device from its conductingcondition to its blocking condition. The resistance valueof theresistance 18 is considerably less than the resistance value of the load14.

FIG. 2 is an l-V curve illustrating the DC. operation of the non-memorytype current controlling device 10 and in this instance the switch 19always remains open. The device 10 is normally in its high resistanceblocking condition and as the DC. voltage is applied to the terminals 15and 16 and increased, the voltage current characteristics of the deviceare illustrated by the curve 20," the electrical resistance of thedevice being high and substantially blocking the current flowtherethrough. When the voltage is increased toa threshold voltage value,the high electrical resistance in the semiconductor materialsubstantially instantaneously decreases in at least one path between theelectrodes 12 and 13 to a low electrical resistance, the substantiallyinstantaneous switching being indicated by the curve 21. This provides alow electrical resistance or conducting condition for conducting currenttherethrough. The low electrical resistance is many orders of magnitudeless than the high electrical resistance. The conducting condition isillustrated by the curve' 22 and it is noted that there is asubstantially linear voltage current characteristicand a substantiallyconstant voltage characteristic which are the same for increase anddecrease in current. In other words, current is conducted at asubstantially constant voltage. In the low resistance current conductingcondition the semiconductor element has a voltage drop which is a minorfraction of the voltage drop in the high resistance blocking conditionnear the threshold voltage value.

As the voltage is decreased, the current decreases along the curve 22and when the current decreases below a minimum current holding value,the low electrical resistance of said at least one path immediatelyreturns to the high electrical resistance as illustrated by the curve 23to re-establish the high resistance blocking condition. In other words,a current is required to maintain the non-memory type currentcontrolling device in its conducting condition and when the currentfalls below a minimum current holding value, the low electricalresistance immediately returns to the high electrical resistance.

The non-memory current controlling device of this invention issymmetrical'in its operation, it blocking current substantially equallyin each direction and it conducting current substantially equally ineach direction, and the switching between the blocking and conductingconditions being extremely rapid. In the case of A.C. operation, thevoltage current characteristics for the second half cycle of the A.C.curreht would be in the opposite quadrant from that illustrated in FIG.2. The A.C. operation of the device is illustrated in FIGS. 3 and4. FIG.3 illustrates the device 10 in its blocking condition where the peakvoltage of the A.C. voltage is below the threshold voltage value of thedevice, the blocking condition being illustrated by the curve in bothhalf cycles. When, however, the peak voltage of the applied A.C. voltageincreases above the threshold voltage value of the device, the device issubstantially instantaneously switched along the curves 21 to theconducting condition illustrated by the curves 22, the device switchingduring each half cycle of the applied A.C. voltage. As the applied A.C.voltage nears zeroso that the current through the device falls below theminimum current holding value, the device switches along the curve 23from the low electrical resistance condition to the high electricalresistance condition illustrated by the curve 20, thisswitchingoccurring near the end of eachhalf cycle.

For a given configurationof the non-memory device 10, the highelectrical resistance may be about 1 megohm and the low electricalresistance about 10 ohms,-

the threshold voltage value may be about 20 volts and the voltage dropacross the device in the conducting condition may be less than 1 volt,and the switching times may be in nanoseconds or less. It has been foundthat by using as the refractory powder particles SnO SiO A1 0 or ZrOextremely satisfactory nonmemory type current controlling devices areobtained. FIG. 5 is an I-V curve illustrating the DC. operation of thememory type current controlling device 10. The

device is normally in its high resistance condition and as the DC.voltage is applied to the terminals 15 and 16 and increased, the voltagecurrent characteristics of the device are illustrated by the curve 30,the electrical resistance of the device being high and substantiallyblocking the current flow therethrough. When the voltage is increased toa threshold voltage value, the high electrical resistance in thesemiconductor element 11 substantially instantaneously decreases in atleast one path between the electrodes 12 and 13 to a low electricalresistance, the substantially instantaneous switching being indicated bythe curve 31. The low electrical resistance is many orders of magnitudeless than the high electrical resistance. The conducting condition isillustrated by the curve 32 and it is noted that there is substantiallyohmic voltage current characteristic. In other words, current isconducted substantially ohmically as illustrated by the curve 32. In thelow resistance curreht conducting condition the semiconductor materialhas a voltage drop which is a minor fraction of the voltage drop in thehigh resistance blocking condition near the threshold voltage value.

As the voltage is decreased, the current decreases along the curve 32and due to the ohmic relation the current decreases to zero as thevoltage decreases to zero. The memory type current controlling devicehas memory of its conducting condition and will remain in thisconducting condition even though the current is decreased tov zero orreversed until switched to its blocking condition as hereafterdescribed. The load line of the load circuit is illustrated at 33, itbeing substantially parallel to the switching curve 31. When a DC.current pulse is applied independently of the load circuit to the memorytype device as by the voltage source 17, low resistance 18 and switch 19in FIG. 1, the load line for such current is along the line 34 sincethere is very little, if any, resistance in this control circuit, and asthe load line 34 intersects the curve 30, the conducting condition ofthe device is immediately realtered and switched to its blockingcondition. The memory type device will remain in its blocking conditionuntil switched to its conducting condition by the reapplication of athreshold voltage to the device through the terminals 15 and 16.

The memory type current controlling device 10 of this invention is alsosymmetrical in its operation, it blocking current substantially equallyin each direction and it conducting current substantially equally ineach direction, and the switching between the blocking and conductingconditions being extremely rapid. In the caseof A.C. operation, thevoltage current characteristics for the second half cycle of the A.C.current would be in the opposite quadrant from that illustrated in FIG.5. The A.C. operation of the memory type device is illustrated in FIGS.6 and 7. FIG. 6 illustrates the device 10 in its blocking conditionwhere the peak voltage of 1 the A.C. voltage is below the thresholdvoltage value of reversal of the current. This symmetrical conductingcondition is illustrated by the curve 32 in FIG. 7.

When the switch 19 is manipulated to apply a current pulse above athreshold current value and the voltage applied to the terminals and 16is below the threshold voltage value, the memory type currentcontrolling device is immediately switched to its blocking condition asillustrated by the curve 30 in FIG. 6. For a given configuration of thememory type device, the high electrical resistance'may be about 1 megohmand the low electrical resistance about 10 ohms,- the threshold voltagevalue may be about volts and the switching times are extremely rapid. Ithas been found that by using TiO as the refractory powder particlesextremely satisfactory memory type ,current controlling devices areobtained. 7

The foregoing operations of the non-memory device and the memory deviceare like those disclosed in the aforementioned patent and, therefore, afurther description thereof is not considered necessary here.

FIG. 8 is an I-V curve illustrating the DC. operation of the non-memorytype current controlling device 10 wherein double switching actions areobtained. The device 10 is normally in its high resistance blockingcondition and as the D.C. voltage is applied to the terminals 15 and 116and is increased, the voltage current characteristics of the device areillustrated by the curve 20, the electricalresistance of the devicebeing high and substantially blocking the current flow therethrough.When the voltage is increased to a first threshold voltage value, thehigh electrical resistance in the semiconductor material substantiallyinstantaneously decreases in at least one path between the electrodes 12and 13 to an intermediate electrical resistance value, the substantiallyinstantaneous switching being indicated by the curve 34. Thisprovides anintermediate electrical resistance condition for'conducting currenttherethrough. This intermediate electrical resistance condition isillustrated by the curve 35. As the voltage is decreased, the currentdecreases along the curve 35 and when the current decreases below aminimum current holding value the intermediate electrical resistance ofsaid at least one path immediately returns to the high electricalresistance as illustrated by the curve 36 to re-establish the highresistance blocking condition. After the device is switched to itsintermediate conducting condition as illustrated by the curve 35 asaforesaid and the voltage is increased to a higher threshold voltagevalue, the intermediate electrical resistance in the semiconductormaterial substantially decreases in at least one path between theelectrodes 12 and 13 to a low electrical resistance, the substantiallyinstantaneous switching being indicated by the curve 21. This provides alow electrical resistance or conducting condition for conducting currenttherethrough. The low electrical resistance is many orders of magnitudeless than the high electrical resistance and the intermediate electricalresistance. This latter conducting condition is illustrated by the curve22 and it is noted that there is a substantially linear voltagecharacteristic and a substantially constant voltage characteristic whichare the same for increase and decrease in current. In other words,current is conducted ata substantially constant voltage. In the lowresistance-current conducting condition as indicated by the curve 22,the semiconductor material has a voltage drop which is a minor fractionof the voltage drop in the high resistance blocking condition near thethresholdvoltage value.

Here, as in the current controlling device whose voltage and currentcharacteristics are illustrated in FIG. 2, the current decreases alongthe curve 22 as the voltage is decreased and when the currentdecreasesbelow a minimum current holding value, the low electricalresistance of said at leastone path immediately returns to the highelectrical resistance as illustratedbythe curve 23 to establish the highresistance. blocking. condition. In other words, asexplained above inconnection with the device whose characteristics are illustrated in FIG.

2, a current is required tomaintain the current controlling device inits conducting condition, and when the current fallsbelow the minimumcurrent holding value, the low electrical resistance immediately returnsto the high electrical resistance. Accordingly, the current controllingdevice whose 1 voltage current characteristics are illustrated in FIG. 8has substantially three electrical resistance conditions. The highelectrical resistance condition illustrated by the curve 20, theintermediate electrical resistance condition illustrated by the curve 35and the low electrical resistance condition illustrated by the curve 22.The device is switched from the low resistance condition to theintermediate resistance condition by the application of a voltage of afirst threshold voltage value and is switched to the low resistancecondition by the application of a voltage of a second or higher voltagethreshold value. In either instance, when the current through the deviceis decreased to a minimum current holding value, the device switchesfrom its intermediate electrical resistance condition or its lowelectrical resistance condition to the high resistance blockingcondition The current controlling device illustrated in FIG. 8 issymmetrical in its operation, it, blocking current substantially equallyin each direction and it conducting current substantially equally ineach direction, and the switching between the high resistance,intermediate resistance and low resistance conditions being extremelyrapid. In the case of A.C. .operation, the voltage currentcharacteristics for the second half cycle of the A.C. current would bein the opposite quadrant from that illustrated in FIG. 8. The A.C.operation ofthis device is illustrated in FIGS. 3, 9 and 10. FIG. 3illustrates the device in its blocking condition where the peak voltageof the A.C. voltage is below the first threshold voltage value of thedevice, the blocking condition being illustrated by the curve 20 in bothhalf cycles. When, however, the peak voltage of the applied A.C. voltageincreases above the-first thresholdvoltage value of the device, thedevice is substantially instantaneously switched along the curves 34 tothe intermediate electrical resistance condition illustrated by thecurves 35, the device switching during each half cycle of the appliedA.C. voltage as illustrated in FIG. 9. As the applied A.C. voltage nearszero so that the current through the device falls. below the minimumcurrent holding value, the device switches along the curve 36 from theintermediate electrical resistance condition to the high electricalresistance condition illustrated by the curve 20, this switchingoccurring during the endof each half cycle. r

When the peak voltage of the applied A.C. voltage increases above thesecond and higher threshold voltage value ofthe device, as illustratedin FIG. 10, the device in addition to switching to the intermediateelectrical resistance condition illustrated by the curve 35 issubstantially instantaneously switched along the curves 21 to theconducting condition illustrated by the curves 22, the device switchingduring each half cycle of the applied AC. voltage. As the applied AC.voltage nears zero so that the current through the device falls belowthe minimum current holding value, the device switches along the curve23 from the low electrical resistance condition to the high electricalresistance condition illustrated by the curve 20, this switchingoccurring near the end of each half cycle.

For a given configuration of the device, whose electricalcharacteristics are illustrated in FIGS. 8 to 10, the high electricalresistance may be about 1 megohm, the intermediate electrical resistanceabout 500 K, and the low resistance about ohms, the first thresholdvoltage value may be about volts and the second threshold voltage valueabout volts, and the voltage drop across the device in the lowresistance conducting condition may be less than 1 volt, and theswitching times may be in nanoseconds or less. It has been found thatwhere ZrO and sometimes A1 0 are used as the refractory powder particlesthese double switching actions may be obtained.

While for purposes of illustration several forms of this invention havebeen disclosed, other forms thereof may become apparent to those skilledin the art upon reference to this disclosure and, therefore, thisinvention is to be limited only by the scope of the appended claims.

We claim:

. l, The method of making a semiconductor element of a currentcontrolling device for an electrical circuit including a semiconductorelement and electrodes in low electrical resistance contact therewith,wherein said semiconductor element has a threshold voltage value and ahigh electrical resistance to provide a blocking condition forsubstantially blocking current therethrough, and wherein said highelectrical resistance in response to a voltage above said thresholdvoltage value substantially instantaneously decreases between theelectrodes to a low electrical resistance which is orders of magnitudelower than the high electrical resistance to provide a conductingcondition for substantially conducting current therethrough, said methodcomprising, substantially individually coating high electricalresistance refractory powder particles with a thin solid coating ofsubstantially V0 within a moler percent range of about 5 to ofsubstantially V0 and forming said semiconductor element from saidsubstantially V0 coated refractory powder particles.

2. The method as defined in claim 1 further comprising, reducing V 0 tosubstantially V0 while individually coating the high electricalresistance refractory powder particles with the solid coating ofsubstantially V0 3. The method as defined in claim 1 further comprising,mixing V 0 powder particles with high electrical resistance refractorypowder particles within a moler percent range of about 5 to 25% of V 0and heating said mixture in a reducing atmosphere to a temperaturebetween the melting point of V 0 and the melting point of V0 to melt theV 0 powder particles and form substantially V0 and individually coat therefractory powder particles with said thin solid coating ofsubstantially V0 4. The method as defined in claim 1 further comprising,mixing V 0 powder particles and V 0 powder particles in substantiallyequal moler percent with high electrical resistance refractory powderparticles within a moler percent range of about 5 to 25% of said V 0 andV 0 and heating said mixture in a substantially inert atmosphere to atemperature between the melting points of V 0 and V 0 and the meltingpoint of VO to melt the V 0 and V 0 powder particles and formsubstantially V0 and individually coat the refractory particles withsaid thin solid coating of substantially V02.

5. The method as defined in claim 1 further comprising, forming a V 0sol having charged V 0 particles colloidally suspended therein, mixinghigh electrical resistance refractory powder particles with said V 0 solfor attracting the charged V 0 particles from said V 0 sol to thesurfaces of said refractory powder particles to provide the same with athin coating of V 0 and drying and heating said mixture in a reducingatmosphere to reduce the V 0 to substantially V0; and individually coatthe refractory powder particles with said thin solid coating ofsubstantially V0 6. The method as defined in claim 5 further comprising,suspending V 0 in water and mixing with H 0 to form a liquid havingperoxyvanadates in solution in the water, boiling the solution todecompose the peroxyvanadates back to V 0 to form the V 0 sol having thecharged V 0 particles colloidally suspended therein.

7. The method as defined in claim 1 wherein said high electricalresistance refractory powder particles comprise SnO SiO A1 0 ZrO orTiO:.

8. The method as defined in claim 1 further comprising, compacting saidsubstantially V0 coated refractory powder particles into a pellet toform said semiconductor element.

9. The method as defined in claim 1 further comprising, mixing saidsubstantially V0 coated refractory powder particles in a high electricalresistance carrier with said coated particles substantially in contactto form said semiconductor element.

lOQThe method as defined in claim 9 wherein said carrier is a paint.

11. The method as defined in claim 9 wherein said carrier is a glass.

1. THE METHOD OF MAKING A SEMICONDUCTOR ELEMENT OF A CURRENT CONTROLLINGDEVICE FOR AN ELECTRICAL CIRCUIT INCLUDING A SEMICONDUCTOR ELEMENT ANDELECTRODES IN LOW ELECTRICAL RESISTANCE CONTACT THEREWITH, WHEREIN SAIDSEMICONDUCTOR ELEMENT HAS A THREHOLD VOLTAGE VALUE AND A HIGH ELECTRICALRESISTANCE TO PROVIDE A BLOCKING CONDITION FOR SUBSTANTIALLY BOLCKINGCURRENT THERETHROUGH, AND WHEREIN SAID HIGH ELECTRICAL RESISTANCE INRESPONSE TO A VOLTAGE ABOVE SAID THREHOLD VOLTAGE VALUE SUBSTANTIALLYINSTANTANEOUSLY DECREASES BETWEEN THE ELECTRODES TO A LOW ELECTRICALRESISTANCE WHICH IS ORDERS OF MAGNITUDE LOWER THAN THE HIGH ELECTRICALRESISTANCE TO PROVIDE A CONDUCTING CONDITION FOR SUBSTANTIALLYCONDUCTING CURRENT THERETHROUGH, SAID METHOD COMPRISING, SUBSTANTIALLYINDIVIDUALLY COATING HIGH ELECTRICAL RESISTANCE REFRACTORY POWDERPARTICLES WITH A THIN SOLID COATING OF SUBSTANTIALLY VO2 WITHIN A MOLERPERCENT RANGE OF ABOUT 5 TO 25% OF SUBSTANTIALLY VO2, AND FORMING SAIDSEMICONDUCTOR ELEMENT FROM SAID SUBSTANTIALLY VO2 COATED REFRACTORYPOWDER PARTICLES.
 2. The method as defined in claim 1 furthercomprising, reducing V2O5 to substantially VO2 while individuallycoating the high electrical resistance refractory powder particles withthe solid coating of substantially VO2.
 3. The method as defined inclaim 1 further comprising, mixing V2O5 powder particles with highelectrical resistance refractory powder particles within a moler percentrange of about 5 to 25% of V2O5, and heating said mixture in a reducingatmosphere to a temperature between the melting point of V2O5 and themelting point of VO2 to melt the V2O5 powder particles and formsubstantially VO2 and individually coat the refractory powder particleswith said thin solid coating of substantially VO2.
 4. The method asdefined in claim 1 further comprising, mixing V2O5 powder particles andV2O3 powder particles in substantially equal moler percent with highelectrical resistance refractory powder particles within a moler percentrange of about 5 to 25% of said V2O5 and V2O3, and heating said mixturein a substantially inert atmosphere to a temperature between the meltingpoints of V2O5 and V2O3 and the melting point of VO2 to melt the V2O5and V2O3 powder particles and form substantially VO2 and individuallycoat the refractory particles with said thin solid coating ofsubstantially VO2.
 5. The method as defined in claim 1 furthercomprising, forming a V2O5 sol having charged V2O5 particles colloidallysuspended therein, mixing high electrical resistance refractory powderparticles with said V2O5 sol for attracting the charged V2O5 particlesfrom said V2O5 sol to thE surfaces of said refractory powder particlesto provide the same with a thin coating of V2O5, and drying and heatingsaid mixture in a reducing atmosphere to reduce the V2O5 tosubstantially VO2 and individually coat the refractory powder particleswith said thin solid coating of substantially VO2.
 6. The method asdefined in claim 5 further comprising, suspending V2O5 in water andmixing with H2O2 to form a liquid having peroxyvanadates in solution inthe water, boiling the solution to decompose the peroxyvanadates back toV2O5 to form the V2O5 sol having the charged V2O5 particles colloidallysuspended therein.
 7. The method as defined in claim 1 wherein said highelectrical resistance refractory powder particles comprise SnO2, SiO2,Al2O3, ZrO2 or TiO2.
 8. The method as defined in claim 1 furthercomprising, compacting said substantially VO2 coated refractory powderparticles into a pellet to form said semiconductor element.
 9. Themethod as defined in claim 1 further comprising, mixing saidsubstantially VO2 coated refractory powder particles in a highelectrical resistance carrier with said coated particles substantiallyin contact to form said semiconductor element.
 10. The method as definedin claim 9 wherein said carrier is a paint.
 11. The method as defined inclaim 9 wherein said carrier is a glass.